SPOILERS BELOW:
Unfortunately Switchblade, you're more than half-way through Episode 1, and the length of the expansion has been the main point of attack for critics and gamers. I, however, feel that my $20 was well-paid, as the return to HL2 gameplay, not to mention useful insight into the storyline, more than made up for the relative shortness of it.
It is incredibly refreshing to return to Half-Life 2, and, while E1 proved to be more taxing on my computer than HL2 (which is odd, as the very small changes made to E1 should not affect performance much), it also proved to be every bit as entertaining. I think E1 was perfect for me because it was exactly what I wanted: more HL2.
Some highlights from my time with HL2:E1
The Stalker train (second'd, while this isn't technically gameplay, it was a creepy, informative and utterly chaotic plot-forwarder that I enjoyed immensely)
Zombine/flashlight wars in the underground (more varieties of brain-eating undead are always appreciated)
The elevator (easily my most enjoyable moment, I would definitely agree. I stockpiled resources by the elevator lift before beginning the zombie sequence, and managed to hold them off fairly effectively with flares for Alyx, flashlight once the flairs were gone, and the occasional shotgun burst)
Taking citizens to the train depot in groups (I took about 15 minutes to get all the items from the surrounding area and transporting them to a single location: this was my refueling line and let me expend vast amounts of ammo on single targets)
Strider battle (very, very rewarding, and an amazing show of level-design)
Ending cinimatic (just as climactic as the endings to HL1 and HL2)